1. Field of the Invention
The present invention relates to an access point in a local area communication network system, more particularly to an access point utilizing a semiconductor optical amplifier capable optical fiber-based ultra-wideband (UWB) wireless communication in an indoor local area communication network system having a transmission speed of at least 100 Mbps using an ultra-wideband communication method.
2. Description of the Related Art
Ultra-wideband communication technology is a wireless communication technology for transmitting large amounts of digital data with a low power in a short distance by means of a wide spectrum frequency. A local area communication network system is a network system capable of performing mutual communication in a local area such as within a building complex, e.g., a house, an office or a hospital.
Such local area communication network systems may utilizing a wireless local area network (hereinafter, referred to as WLAN), which can transceive data through wirelessly. The WLANs in the local area communication network system maybe capable of a maximum transmission speed of 22 Mbps using a 2.4 GHz ISM (industrial, scientific and medical) band. Efforts to improve the transmission speed of such WLANs (e.g., a transmission speed of 54 Mbps at maximum in the 5 GHz band and a transmission speed more than 54 Mbps in millimeter wave band (30 GHz ˜300 GHz)) are under development, but not yet perfected.
In currently available WLANs in local area communication network systems, a radio frequency (RF) signal with a frequency band of 2.4 GHz or 5 GHz is usually used as a carrier for carrying data. Since such WLANs have a superior mobility and has no cable connection in contrast with a wired LAN, the WLAN is generally preferable users.
It is also noted that according to the 802.11 ab/g standard, a WLAN is generally limited to have a maximum transmission speed of 54 Mbps. This limitation to the transmission speed of the WLAN may cause a bottleneck phenomenon in high speed and high capacity services provided through the existing WLAN by the fiber to the home (FTTH), so that it is nearly impossible to provide a satisfactory service to a home or office environment. In an attempt to solve such problems, an ultra-wideband signal has been used instead of a radio frequency signal band as a transmission medium in the WLANs. The transmission speed of the WLAN using the ultra-wideband signal as the transmission medium is at least 100 Mbps. In the ultra wideband-based WLAN, high speed and high capacity services are possible, but service area is limited to 10 m.
FIG. 1 is a diagram showing an example of a wireless network system for providing an ultra wideband-based WLAN service in the inside of a building.
As shown in FIG. 1, the wireless network system includes one central station (hereinafter, referred to as CS) 10 and a plurality of access points (hereinafter, referred to as AP) 22, 32 and 42. The CS 10 is connected to the APs 22, 32 and 42 through an optical fiber. The APs 22, 32 and 42 respectively construct sub-networks 20, 30 and 40 with respect to areas which are served by each of the APs 22, 32 and 42.
In FIG. 1, the APs 22, 32 and 42 are connected to the CS 10 through an optical fiber to construct a first sub-network 20, a second sub-network 30 and a third sub-network 40, respectively. In the first sub-network 20, a first AP 22 and a projector 24 perform ultra-wideband communication. In the second sub-network 30, a second AP 32, a television 34 and a notebook 36 perform ultra-wideband communication. In the third sub-network 40, a third AP 42, a computer 44 and a facsimile 46 perform ultra-wideband communication.
Also, a ultra-wideband signal is respectively transmitted from the CS 10 to the APs 22, 32 and 42 through an optical fiber. Further, high capacity services are provided to the CS 10 through a fiber-to-the-home (FTTH). The CS 10 may provide several services, such as a multi-media service, a video on demand (VOD), an education on demand (EOD) and an audio on demand (AOD), which can be provided by the FTTH, to the APs 22, 32 and 42 or terminals without service collision.
As shown in FIG. 1, in the ultra-wideband wireless network system, a plurality of APs 22, 32 and 42 are connected to one CS 10. Accordingly, in the ultra-wideband wireless network system, in order for the APs 22, 32 and 42 to be commercially competitive they need to be inexpensive to the user, light, small, consume low power and easy to use.
Conventional APs generally use a laser diode (hereinafter, referred to as LD) and a photodetector (hereinafter, referred to as PD, or an electro-absorption modulator (hereinafter, referred to as EAM).
In this regard, the APs that use the LDs and the PDs are the most common. In the AP, each LD and PD needs a driving circuit for driving the LD and the PD, an automatic temperature control (ATC) circuit for controlling an temperature of the LD and the PD, and an automatic power control (APC) circuit for controlling a supply of a power necessary for operating the LD and the PD.
Since many modules in the AP are necessary as described above, the size of the AP grows larger. Further, the conventional AP consumes a large amount of power to drive many modules.
In order to solve the problems occurring in APs using conventional LDs and PDs, an AP constructed by only single optical device, which can perform functions of a light source and an optical modulator at the same time, is known. This is an AP using the EAM, which is a single optical device. The EAM operates as the PD and the optical modulator according to the size of an applied reverse bias voltage.
However, when sufficient optical power is not input to the EAM, which may be due to an optical loss between a CS and an AP, an AP using the EAM has difficulty in operating as an PD and an optical modulator. In order to solve such problem, the CS must include an optical amplifier, which enables an optical power to be sufficiently transmitted to the AP, in consideration of the optical loss.
FIG. 2 is a block diagram showing an example of AP using a conventional LD and PD. Referring to FIG. 2, functions of each module according to a transmission of ultra-wideband signal are described according to each of downstream and upstream transmissions.
When an ultra-wideband signal is transmitted downward, an LD 13 in a CS 10 performs conversion in an ultra-wideband communication method through an optical fiber according to a driving signal input from an LD driver 12. It converts the ultra-wideband signal into an optical signal by performing a direct intensity modulation of the ultra-wideband signal. A splitter 15 transmits the converted optical signal to an AP 20 through an optical fiber.
A combiner 25 in the AP 20 transmits the received optical signal to a PD 22. The PD 22 converts the received optical signal into an electrical signal. A high-gain amplifying unit 23 amplifies the converted electrical signal to a level sufficient for a wireless transmission. A diplexer 24 sends the high-gain amplified ultra-wideband signal into the air through an antenna.
When the ultra-wideband signal is transmitted upward, ultra-wideband signal is received by an antenna. The diplexer 24 transmits the received ultra-wideband signal to a low noise amplifying unit 29. The low noise amplifying unit 29 low-noise amplifies the received ultra-wideband signal and outputs the amplified signal to an LD driver 28. The LD driver 28 generates a current corresponding to the low-noise amplified ultra-wideband signal and provides the generated current to an LD 27. The LD 27 generates an optical signal corresponding to the received current. The combiner 25 transmits the optical signal generated by the LD 27 to the CS 10 through an optical fiber.
The splitter 15 in the CS 10 receives the optical signal transmitted through the optical fiber and transmits the received optical signal to a PD 18. The PD 18 converts the received optical signal into an electrical signal. The high-gain amplifying unit 17 amplifies the converted electrical signal to a predetermined level and outputs the amplified signal to a module which demodulates amplified signal.
As described above, in constructing the AP using conventional LDs and PDs, the LDs and the PDs must be respectively included in each AP connected to the CS 10.